All references cited in this specification, and their references, are incorporated by reference herein where appropriate for teachings of additional or alternative details, features, and/or technical background.
Disclosed in the embodiments herein is a system for protecting the face of a printhead, in particular a solid ink jet printhead printing on an image transfer member, from contaminants. Such system comprises a sticky baffle placed in close proximity to the surface of an image transfer surface superior to the printhead.
For printing in a solid-ink printer, the simplest method of producing an output image is to propel droplets of ink onto a piece of paper to directly print the image onto the paper, i.e., a process known as direct printing. However, direct printing has many disadvantages. First, the head to paper gap must be adjusted for different media in order to control drop position. Second, there is the well-known paper hand-off problem between the rollers that guide the paper, because of the large size of the head. Third, there is a concern that head reliability will decrease because the paper is near the head. Also, to maximize print speed, many direct print architectures deposit the image bi-directional, which introduces image artifacts and color shifts. These problems are addressed with an offset, or indirect printing process. In this process, the ink is first applied to a rotating drum or other intermediate support surface and then transfixed off onto the paper wherein the ink goes on hot and then is fused. Therefore, a single drum surface transfers the image, spreads the ink droplets, penetrates the ink into the media, and controls the topography of the ink to increase paper gloss and transparency haze.
The process requires a delicate balance of drum temperature, paper temperature, transfix load, drum and transfix roller materials and properties thereof in order to achieve image quality.
To solve some of the above stated problems, ink jet printing systems have utilized intermediate transfer ink jet recording methods, such as that disclosed in U.S. Pat. No. 5,389,958. The intermediate transfer surface is applied by a wicking pad that is housed within an applicator apparatus. Prior to imaging, the applicator is raised into contact with the rotating drum to apply or replenish the liquid intermediate transfer surface.
Once the liquid intermediate transfer surface has been applied, the applicator is retracted and the print head ejects drops of ink to form the ink image on the liquid intermediate transfer surface. The ink is applied in molten form, having been melted from its solid state form. The ink image solidifies on the liquid intermediate transfer surface by cooling to a malleable solid intermediate state as the drum continues to rotate. When the imaging has been completed, a transfer roller is moved into contact with the drum to form a pressurized transfer nip between the roller and the curved surface of the intermediate transfer surface/drum. A final receiving substrate, such as a sheet of media, is then fed into the transfer nip and the ink image is transferred to the final receiving substrate.
FIG. 1 (prior art) is an overall perspective view of an offset phase change ink jet printing apparatus, generally indicated by the reference numeral 1. An example of an offset phase change ink jet printer is disclosed in U.S. Pat. No. 5,389,958.
FIG. 3 (prior art) illustrates the inner works of solid ink jet systems that may be employed in the housing shown in FIG. 1 employing an image transfer drum.
Referring to FIG. 3, there is shown a print head 11 having ink jets supported by appropriate housing and support elements (not shown) for either stationary or moving utilization to deposit ink droplets in image configuration onto an intermediate transfer surface 12.
For hot melt or solid ink based systems, the ink utilized is preferably initially in solid form and then changed to a molten state by the application of heat energy to raise the temperature from about 85 degrees to about 150 degrees centigrade. In various embodiments, the temperature may be lower or higher, but this range is preferred. Elevated temperatures above this range may cause degradation or chemical breakdown of inks currently in use. The molten ink is then applied in raster fashion from ink jets in the print head 11 to the intermediate transfer surface 12 forming an ink image. The ink image is then cooled to an intermediate temperature and solidifies to a malleable state wherein it is transferred to a receiving substrate 28 such that the pixels are not spread and an initial matte finish is achieved.
The intermediate transfer surface 12 may be provided in the form of a drum, as shown in FIG. 3, but may also be provided as a web, platen, belt, band or any other suitable design. The drum 14 may be fabricated out of any metallic material and most preferably is made from aluminum and polished to a high gloss. The intermediate transfer surface may also be coated with an elastomer layer 8, which defines a release surface. In addition, the intermediate transfer surface 12 may be coated with a liquid release layer applied to the drum 14 by contact with an applicator assembly 16, such as a liquid impregnated web, wicking pad, roller or the like. By way of example, but not of limitation, applicator assembly 16 comprises a wicking roller or pad of fabric or other material impregnated with a release liquid for applying the liquid and a metering blade 18 for consistently metering the liquid on the surface of the drum 14. Suitable release liquids that may be employed to coat the intermediate transfer surface 12 include water, fluorinated oils, glycol, surfactants, mineral oil, silicone oil, functional oils or combinations thereof. As the drum 14 rotates about a journalled shaft in the direction shown in FIG. 3, applicator assembly 16 is raised by the action of an applicator assembly cam and cam follower (not shown) until the wicking roller or pad is in contact with the surface of the drum 14. The release liquid, retained within the wicking roller or pad is then deposited on the surface of the drum 14.
The intermediate transfer surface 12 may be heated by an appropriate heater device 19. The heater device 19 may be a radiant resistance heater positioned as shown or positioned internally within the drum 14. In a preferred embodiment incorporating solid ink based ink jet technology, the heater device 19 may increase the temperature of the intermediate transfer surface 12 from ambient temperature to between 25 degrees to about 70 degrees centigrade or higher for receiving the ink from print head 11. This temperature is dependent upon the exact nature of the liquid employed in the intermediate transfer surface 12 and the ink used and can be adjusted by providing an optimal temperature controller 40 in combination with a thermistor 42. Ink is then applied in molten form from, for example, about 85 degrees to about 150 degrees centigrade to the exposed surface of the intermediate transfer surface 12 by the print head 11 forming an ink image 26. The ink image 26 solidifies on the intermediate transfer surface 12 by cooling down to the malleable intermediate state temperature provided by heating device 19.
After the ink image is created on the intermediate transfer surface, the image is then transferred to a receiving substrate 28. A receiving substrate guide apparatus 20 may transport the receiving substrate 28, such as paper or transparency, from a positive feed device (not shown) and guides it through a nip 29 formed between drum 14 and transfer roller 23. Thus, opposing arcuate surfaces of the transfer roller 23 and the drum 14 forms the nip 29. The transfer roller 23 may have a metallic core, preferably steel with an elastomer coating 22. The drum 14 continues to rotate, entering the nip 29 formed by the transfer roller 23 with the curved surface of the intermediate transfer surface 12 containing the ink image 26. The ink image 26 is then deformed to its image conformation and transferred to the receiving substrate 28 such that the pixels formed by the ink image on the receiving substrate are not spread creating an initial matte finish. The elastomer coating 22 on roller 23 engages the receiving substrate 28 on the reverse side to which the ink image 26 is transferred.
In this process, the ink image 26 is first applied to the intermediate transfer surface 12 of the rotating drum 14 and then transfixed off onto the receiving substrate 28 having a pixel image. Stripper fingers 25 (only one of which is shown) may be pivotally mounted to the imaging apparatus 10 to assist in removing any paper or other final receiving substrate 28 from the exposed surface of the intermediate transfer surface 12.
Heater 21 may be used to preheat the receiving substrate 28 prior to the transfer of the ink image 26. The thermal energy of the receiving substrate 28 is preferably kept sufficiently low so as not to melt the ink image upon transfer to the receiving substrate 28. When the ink image 26 enters the nip 29 it is deformed to its image conformation and adheres to the receiving substrate 28 either by the pressure exerted against ink image 26 on the receiving substrate 28 or by the combination of the pressure and heat supplied by heater 21 and/or heater 19. Heater 24 may be employed which heats the transfer roller 23. Heater devices may also be employed in the paper or receiving substrate guide apparatus 20 and/or in the transfer and fixing roller 23, respectively. The pressure exerted on the ink image 26 must be sufficient to have the ink image 26 transfer to the receiving substrate 28.
A general problem in ink jet printers printing on an image transfer member, in particular solid ink jet printers or so-called phase change ink jet printers, is that the paper in its movement through the printer may introduce paper particle contamination into the inner machine environment where such contamination may reach the nozzle faces of the printheads, causing temporary or permanent jet deflections or outages. FIG. 2 (prior art) shows a front plan view of an orifice plate 7 that forms part of an ink jet print head (not shown). An example of a suitable ink jet print head is found in U.S. Pat. No. 5,677,718. The orifice plate 7 includes multiple rows of multiple orifices 5. The print head ejects ink from orifices 5 to create an image on an intermediate transfer surface (not shown), such as silicone oil. The image is then transferred to a final receiving medium, such as a sheet of paper. There is needed a low cost contamination abatement system which traps contaminants before they can reach the printhead.